【作者】 王俊；

【导师】 吕清刚；

【作者基本信息】 中国科学院研究生院（工程热物理研究所） ， 热能工程， 2011， 博士

【摘要】 我国电力工业发展迅速,发电机组在往大容量和大机组方向发展,污染物排放标准更加严格。电力工业对煤粉燃烧提出更高要求：燃烧稳定、低污染、适应负荷变化。电力工业发展导致优质动力煤供应趋紧,而无烟煤在我国储量丰富,占火力发电的比重将越来越高。无烟煤难以着火、难以稳燃、难以燃尽的特性,导致燃用无烟煤的锅炉存在燃烧效率低、NOx排放高以及低负荷下燃烧不稳等问题。本论文提出了将无烟煤粉在进入燃烧室燃烧前先经过循环流化床在低空气当量比下预热的新工艺,并描述了对此新工艺开展的一系列试验研究。无烟煤粉在循环流化床内经过加热、挥发分析出、部分气化、部分燃烧等物理化学过程,发生粒径减小、比表面积增大、总孔体积增大、温度超过800℃等变化,预热后的燃料再进入燃烧室燃烧,燃烧稳定,NOx排放低。设计建造了30kW无烟煤粉循环流化床预热燃烧试验系统。循环流化床提升管的直径为90mm、高度为1500mm,下行燃烧室的直径为260mm、高度为3000mm。在试验系统上,对我国最典型的动力无烟煤——阳泉煤进行了一系列改变燃烧控制参数和空气分级参数的试验。结果表明：采用预热后燃烧的工艺,可以使挥发分含量仅6.74%的无烟煤在循环流化床预热到800℃以上；预热后的高温燃料在下行燃烧室燃烧具有良好的稳定性和温度分布均匀性,下行燃烧室最大温差低于200℃；预热后的高温燃料中的颗粒粒径比加入循环流化床的无烟煤粉粒径显著减小,50%切割粒径d50从82μm降低到19μm,比表面积显著增大,从4.9m2/g增大到111.0m2/g,总孔体积也明显增加,从0.014cm3/g提高到0.096cm3/g；预热产生的烟气中包含部分可燃气体,换算到干冷状态下的低位发热量为1.53MJ/Nm3；减小加入循环流化床的无烟煤粉粒径,有利于提高燃烧效率；只要总过量空气系数和预热温度在合理范围内,改变这两个参数对无烟煤粉的燃烧特性影响不大；阳泉无烟煤粉在本试验台上的燃烧效率达到94.17%。预热燃料在下行燃烧室燃烧,燃料N向NOx的转化率低于32%,尾部烟气排放NOx浓度不高于400mg/m3；随着加入循环流化床无烟煤粉粒径的减小、还原区空气当量比的增大以及燃料在还原区停留时间的缩短,尾部烟气NOx排放增大；系统总过量空气系数对NOx排放浓度的影响不大。更多还原

【Abstract】 With the rapid development of electric power industry in China, generator sets are required to be developed of bigger capacity and lower emission level. Thus some higher requirements of coal combustion were put forward, such as burning stability, low pollution and flexibility of boiler load variation. Electric power industry development also leads to the lack of high quality power coal. Since the anthracite coal reserves in China are large, it can be seen that the percentage of anthracite in thermal power plant fuel will be increasing continuously. However, anthracite has some intrinsic problems for combustion. It is difficult to ignite, to combust stably and to burn out. Such features will make the boiler, which burning anthracite, experiences low combustion efficiency, high NOx emissions and unstable combustion in low boiler load.A new technology based on pulverized coal preheated by circulating fluidized bed (CFB) was proposed in this thesis. In the CFB, the properties of pulverized anthracite coal changed through some physical and chemical reactions, such as friction, devolatile, pyrolysis and partial combustion. These changes of property include diameter of pulverized anthracite coal decreasing, specific surface area increasing, pore volume increasing, temperature increasing up to800℃, which are advantaged to stable combustion. The preheated pulverized anthracite entered the combustion chamber to combust, with low NOx emissions.A30kW bench-scale rig of pulverized anthracite combustion in a down-fired combustion chamber (DFCC) was developed. The CFB riser has a diameter of90mm and a height of1,500mm. The down-fired combustion chamber has a diameter of260mm and a height of3,000mm.A series of experiments were carried out by the parameters variation of combustion and air-staged. The results showed that Yangquan anthracite with volatile as air dry basis6.74%can be preheated up to800℃in CFB. The combustion of preheated pulverized anthracite was stable and uniform with the maximum temperature difference less than200℃; the size of preheated pulverized anthracite significantly decreased, the50%cut size decreased from82μm to19μm after preheating. The specific surface area increased from4.9m2/g to111.0m2/g, and the pore volume increased from0.014cm3/g to0.096cm3/g. The gas generated in preheating process included combustible gas, whose net calorific value is1.53MJ/Nm3. Combustion efficiency increased when the size of pulverized anthracite feed into the CFB decreased. As long as the variations of excess air ratio and temperature of preheated pulverized anthracite were in a reasonable scope, these two parameters have little impact on combustion efficiency. Combustion efficiency of Yangquan pulverized anthracite in this30kW bench-scale rig was94.17%.As a result of air-staged combustion, the conversion ratio of fuel-N to NOx was less than32%, and the NOx concentration was less than400mg/m3. The NOx concentration increased with the size of pulverized anthracite decreased, air ratio in the reducing zone increased and the residence time shortened. The excess air ratio has little effect on NOχ concentration.更多还原